As is known, mechanical and/or thermal methods are used to isolate valuable ingredients from a large number of different biological materials, in particular raw plant materials such as agriculturally obtained fruit. In order to be able to separate off these ingredients from the biological material, the membranes of the cell material, in particular of the plant cell, have in every case to be opened. As a rule, this takes place by the action of mechanical forces such as chopping, grinding, rolling, etc. Other methods for disrupting the cell membranes of the biological material are thermal disruption, with the cell membranes being denatured by the influence of temperature, or a combination of thermal methods and mechanical methods. Following on from the disruption process, the soluble ingredients of the biological material are pressed out, extracted with solvent, usually water, or, in the case of insoluble substances, flushed out.
Such methods for isolating ingredients from biological material are particularly relevant for the sugar industry since, as is known, it is necessary, for the purpose of obtaining sugar (sucrose) in central Europe, to process sugar beet (Beta vulgaris) using these methods in order to obtain the sugar from the beet. In this connection, the washed beet are traditionally chipped in conventional cutting machines and the resulting chips are scalded, in a chip mash, with hot water at approximately 70 to 75° C. During this procedure, the beet cells are thermally denatured, i.e. the cell walls become disrupted and thereby permeable to sucrose molecules. In a subsequent extraction process, usually performed by means of countercurrent extraction, a sucrose-containing extract (raw juice) is obtained at temperatures of from approximately 68 to 70° C.
As is known, a substantial proportion of extraneous water (condensate) has to be added for the extraction to be effective. In order to optimize the extraction process and reduce the residual content of sugar in the extracted chips, approximately 105% to 110% raw juice, in relation to the quantity of chips, is usually withdrawn in the known methods. The withdrawal is calculated from the ratio of the quantity of extract to the quantity of beet employed. After that, a juice clarification of the extract can be carried out.
In addition to the substantial quantity of extraneous water which is required for the extraction, the processing of biological material for the purpose of isolating the ingredients is also a process which consumes a great deal of energy. In particular, the thermal disruption of the biological material at customary temperatures of more than 70° C. demands a high energy input. However, a substantial proportion of extraneous water also has to be heated to temperatures of more than 70° C. for the extraction step which follows and then evaporated once again at high energy cost in the subsequent course of the process. There is therefore a need, from the prior art, to disrupt biological material, in particular sugar beet or sugar beet cells, with a low consumption of energy and, by means of using a suitable downstream method, to reduce the quantity of water and energy which is required for isolating the ingredients from the biological material.
Another and important aspect is the extent to which the extracted biological material can be dewatered. For example, about 27 million tons of sugar beet are processed annually in the Federal Republic of Germany for the purpose of obtaining sugar. Following the aqueous countercurrent extraction of the comminuted beet, 15 million tons of extracted chips which have a water content of about 90% and which are used as cattle feed then accrue. In order to make the product stable and transportable, it has to be extensively dewatered. The dewatering firstly takes place mechanically, by means of pressing, and then by drying down to a residual water content of about 10%. In principle, a higher degree of pressing-out means a higher consumption of electrical energy, which consumption has to be set against the reduced consumption of fuel for the drying. Since the costs of the mechanical dewatering up to a dry matter content of what has previously been about 35% are markedly more advantageous than those for the drying, improving the pressing-out is a consistent aim of the sugar industry. The cost pressure in connection with the drying, and the environmental protection measures associated therewith, have led to the mechanical dewatering being steadily improved. The average dry matter content of pressed chips, as determined in 16 selected factories, rose from barely 20% in 1976 to on average approx. 32% in 1987. While about 44% of the water which has been carried through together with the extracted chips has still to be removed after the extracted chips have been pressed out to give a dry matter content of 20%, this proportion of water has already fallen to approx. 25% when pressing out has taken place to give 30% dry matter. This represents a substantial saving on energy which can amount to approx. 500 000 EUR per season (assumed oil price: 150 EUR/ton) in the case of a factory which processes 10 000 tons of beet per day. There is, therefore, an urgent need to further improve the ability of the biological material, in particular of the sugar beet chips, to be pressed out, that is to be dewatered, after the extraction.